1. Field of the Invention
The present invention is directed generally to a wireless communication system, a wireless host, and a wireless device, in particular, is directed to a wireless USB host, and a wireless USB device for carrying out wireless communication in compliance with wireless USB standard.
2. Description of the Related Art
Wireless universal serial bus (USB) is a technical standard that is introduced as an extension of the USB, which is widely used as a standard for wired, short-range communications, and that provides ease of use of wireless communication while preserving security and speed of wired communications. Specification for wireless USB has been defined by the Wireless USB Promoter Group, which is a lower branch of the USB-Implementers Forum (USB-IF).
Wireless USB employs a wireless technology called Ultra-wideband (UWB). UWB operates in a broad spectrum of 3.1 to 10.6 gigahertz (GHz). IEEE 802.15.3a Task Group in the Institute of Electrical and Electronic Engineers (IEEE) formulating standards works for standardization of the physical layer of UWB. There are two modulation approaches, specifically Direct Spread-UWB (DS-UWB) and Multiband-Orthogonal Frequency Division Multiplexing (MB-OFDM), for the physical layer of UWB.
In DS-UWB, two bands (dual band), or specifically, a low band of from 3.1 to 4.9 GHz and a high band of from 6.2 to 9.7 GHz are used. Data transmission is performed by performing primary modulation by using quadrature phase shift keying (QPSK) or binary phase shift keying (BPSK), and thereafter secondary modulation by using code division multiple access (CDMA). At this time, the data transmission is performed by using direct-sequence spread-spectrum technique.
In MB-OFDM, the spectrum of from 3.1 to 10.6 GHz is divided into 14 bands (frequency bands). For each band, primary modulation is performed by QPSK to thereby superimpose digital signals on radio waves first. Subsequently, secondary modulation is performed by OFDM to realize communication that is highly tolerant to interference with other radio waves. Specification for MB-PFDM physical (PHY) layer has been defined as the WiMedia PHY by a group called the WiMedia Alliance.
By performing modulation by using these modulation methods, transmitting electric power consumption per megahertz (MHz) is lowered in the UWB. Specifically, the Federal Communications Commission (FCC) has defined that the equivalent isotropic radiated power (EIRP), which denotes a limit of transmitting electric power consumption level for UWB communications, per megahertz is to be equal to or below −41.25 decibel per milliwatt (dBm). This can be converted into total electric power of approximately 0.5 milliwatt (mW), which is approximately one-twentieth of that of IEEE 802.11b wireless LAN and personal handy-phone system (PHS), which is 10 [mW].
The WiMedia Alliance has defined protocol for the media access control (MAC) layer as the WiMedia MAC. Wireless USB is based on wireless technologies, or specifically the WiMedia PHY and the WiMedia MAC, and incorporates USB technology based on the Universal Serial Bus Specification Revision 2.0 (USB 2.0 specification) defined by the USB-IF for wired communication. Accordingly, if the communication range is equal to or less than three meters, wireless USB allows data transfer of 480 megabits per second (Mbps), which is the maximum data transfer rate of the wired USB 2.0.
Wireless USB has low transmitting power consumption, which is one of characteristics of UWB. Hence, wireless USB is ranked as a personal area network (PAN) where radio waves are assumed to reach a range of up to 10 meters. Wireless USB can be said to be, in addition to providing higher data throughput, less susceptible to eavesdropping, and more secure than wireless LAN.
However, because wireless USB is one of the wireless communications technologies, a disadvantageous case that, for instance, a user that has not an access right or a permission accesses a file in a storage, which corresponds to a wireless USB device, without being noticed by an authorized user can occur. To this end, a wireless USB desirably has a function of authenticating an authorized user.
In wireless USB, the authentication is performed by using what is called a 4-way handshake scheme illustrated in FIG. 15 between a wireless USB host and a wireless USB device. The 4-way handshake is performed using four messages, or specifically, a message 1, a message 2, a message 3, and a message 4. The wireless USB host and the wireless USB device shares a connection key (CK) before the 4-way handshake is started. The wireless USB host generates a random number called HNonce; the wireless USB device generates a random number called DNonce. As the message 1, the wireless USB host transmits the HNonce to the wireless USB device (Step S400). The wireless USB device calculates a pairwise temporary key (PTK) by combining its own DNonce, the received HNonce, and the CK together (Step S402) based on a predetermined equation. The thus-obtained PTK is utilized as an encryption key in data transfer to be performed later.
Similarly, as the message 2, the wireless USB device transmits the DNonce to the wireless USB host (Step S404). The wireless USB host calculates a PTK by combining the received DNonce, its own HNonce, and the CK together (Step S406) based on the same equation. Thereafter, the PTK calculated by the wireless USB host is sent out by the wireless USB host as the message 3 (Step S408), and the PTK calculated by the wireless USB device is sent out by the wireless USB device as the message 4 (Step S410). The wireless USB host and the wireless USB device individually determine whether the calculated PTK and the received PTK has match (Step S412, Step S414). If the two PTKs match (Yes at Step S412, Yes at Step S414), communication between the wireless USB host and the wireless USB device is started. Authentication by using the 4-way handshake is performed in this manner. In this way, the 4-way handshake premises that a CK is pre-shared between a wireless USB host and a wireless USB device.
As illustrated in FIG. 16, a CK is defined in the Wireless Universal Serial Bus Specification, Revision 1.0 (hereinafter, “wireless USB 1.0 specification”) as a component that, together with a connection host identifier (CHID) serving as an identifier of the wireless USB host and a connection device identifier (CDID) serving as an identifier of the wireless USB device, constitutes a connection context (CC). The CK is shared between the host and the device as a result that the CC is shared therebetween prior to authentication. In the wireless USB 1.0 specification, the term “association” is used to describe a series of operations that are performed to share a CC. Specification of the association is defined in Association Models Supplement to the Certified Wireless Universal Serial Bus Specification (hereinafter, “association specification”), which is a supplemental document of wireless USB.
In the association specification, two association models, more specifically the Cable Association Model and the Numeric Association Model, are described.
In the Cable Association Model, first-time association between a wireless USB host and a wireless USB device is performed by using a USB cable in a wired manner. The wireless USB host provides the wireless USB device with a CC via the USB cable. This causes the CC to be shared between the host and the device.
In contrast, in the Numeric Association Model, at first-time association between a wireless USB host and a wireless USB device, buttons, provided on each of the device and host, for starting association are pressed, and then each of the wireless USB host and the wireless device generates a random number. The host and the device exchange the random numbers by radio waves. Each of the wireless USB host and the wireless USB device displays a numeric value calculated from the random number generated by itself and the received random number by using a predetermined equation. A user checks whether the numeric values displayed on the wireless USB host and the wireless USB device match. If the numeric values match, buttons, which are provided on the wireless USB host and the wireless USB device, for permitting association are independently pressed. Thereafter, the wireless USB host provides the wireless USB device with a CC by radio waves, whereby the CC is shared between the device and the host.
However, each of the two association model has disadvantage discussed below. With the Cable Association Model, it is an essential condition that a wired USB port is additionally provided on each side of the wireless USB host and the wireless USB device. Furthermore, connection with a cable is troublesome. Meanwhile, with the Numeric Association Model, it is an essential condition that each of the wireless USB host and the wireless USB device includes a display. This makes the Numeric Association Model less appropriate for adoption into a small device, such as USB memory.
In view of the above circumstances, Near Field Communication Association Model (hereinafter, “NFC”) is defined as a new association model in the wireless USB 1.1 specification, which is a currently drafted specification as a succeeding version of the wireless USB 1.0. NFC is a short-range two-way wireless communication standard that allows communication at a rate of from 100 to 400 kilobits per second (Kbps) over a short distance of approximately 10 centimeters by using radio waves of the 13.56 MHz. NFC is a communication technology that has originally been used in contactless IC cards for use in an automatic checking and collecting machine in a station, or the like. Because NFC was approved as an international standard as ISO/IEC 18092, NFC can proliferate in electronics products, such as audio equipment, for general end consumers.
Using NFC as one of association models for providing a CC from a wireless USB host to a wireless USB device is contemplated in wireless USB technology. Specifically, this scheme is performed such that, if it is desired that data in a notebook personal computer (PC) corresponding to a wireless USB host is printed by a printer corresponding to a wireless USB device, the notebook PC and the printer are brought into a range of 10 centimeters or less, thereby causing the notebook PC and the printer to share a CC by NFC.
As one of such techniques that use NFC, a technique directed to wireless local area network (LAN) technology is disclosed in Japanese Patent Laid-open Publication No. 2007-166538. According to this technique, communication methods supported by two wireless LAN communication devices are determined by using NFC, first. If the communication methods match, communication is carried out by using the communication method; if the communication methods do not match, communication is carried out by NFC. Another technique of causing two wireless communication devices to carry out communication by NFC first, and, if the two wireless communication devices support higher-speed communication protocol, such as Bluetooth®, switching communication protocol to the higher-speed communication protocol is disclosed in Japanese Patent Laid-open Publication No. 2008-160856. A technique that uses NFC in Device Wire Adapter (DWA) is disclosed in Japanese Patent Laid-open Publication No. 2008-72533. DWA acts as an adapter that converts data, in order to communicate data from external equipment, which is connected to a USB connector, by wireless USB communication.
As discussed above, NFC is an association model that complements disadvantages of the Cable Association Model and the Numeric Association Model. However, operation to be performed to verify whether a wireless USB host that has attempted association is an authorized wireless USB host is not defined in NFC.
Hence, such a situation that a user of a wireless USB host who is not given an access right to a wireless USB device that employs NFC as its association model establishes association with the wireless USB device by NFC in a sneaky manner when the user is unaccompanied by other people can occur. This allows the user that is not given an access right to deliver a CC to the wireless USB device and carry out communication between the wireless USB host and the wireless USB device, which is undesirable.
For instance, assume that a laboratory in a university has a printer corresponding to a wireless USB device that employs NFC for an association model. It is highly possible that a room where the printer is installed is left unlocked in many cases because of the way the printer is used. Under such a condition, there can occur such an undesirable situation that, for instance, due to a meeting attended by all members of the laboratory held in another room, the room where the printer is installed is emptied continuously for several hours, during which an outsider, such as a staff of another laboratory, carries a notebook PC into the room, establishes association with the printer without permission, and performs a large amount of printing by using the printer.
The present invention has been conceived in view of the above circumstances and aims at providing a wireless communication system, a wireless host, a wireless device, and a wireless communication method capable of restricting association to be established between a wireless host and a wireless device in response to an instruction issued by a user of a wireless host who does not have an access right to the wireless device.